Template type deduction in C++ for Class vs Function?

Question

Why is that automatic type deduction is possible only for functions and not for Classes?

Answer 1

At Kona meeting Template parameter deduction for constructors (P0091R0) has been approved, which means that in C++17 we'll be able to we can write:

pair p1{"foo"s, 12};
auto p2 = pair{"foo"s, 12};
f(pair{"foo"s, 12});